Mt Rouse from the Hamilton Road. The line running diagonally across the side of the mountain is a walking track from the car park at the base to the lookout on top.

The steep slope of the scoria cone can be clearly seen at the top of Mt Rouse.

The cutting for the footpath across the side of the mountain shows scoria below the surface.

Mt Rouse is one of several extinct volcanoes in the Victorian Western District near Hamilton and beside the township of Penshurst. When it was active, Mt Rouse was a composite volcano ejecting flowing lava and scoria at different times. The main, steep sided cone of scoria, with the lookout and telecommunications towers on top, is composed mainly of red, brown and grey scoria. This main cone is crescent shaped around a breach opening to the south-west. South of the main cone is a deep circular crater extending below the level of surrounding lava flows. This crater, rimmed with basalt and red scoria outer walls, is probably the source for most of the lava flows that spread out as "stony rises" from the mountain.
While Mt Rouse was erupting, molten magma forced up from deep underground and reaching the surface under pressure was ejected in a lava fountain reaching several hundred metres into the air. As the lava fell back to earth it frothed and solidified into scoria forming a cone around the crater. While the eruption continued the crater filled with lava and the cone grew higher until the lava lake in the crater broke through the scoria wall and flowed away leaving the still visible breach. Towards the end of the eruption, liquid lava flowed over scoria near the base of the cone; the layer of basalt on top of several metres of scoria can be seen in the walls of the quarry near the road entrance.

A substantial volume of lava was ejected from Mt Rouse, enough to reach Port Fairy 60 kilometres away where lava from Mt Rouse has been identified at the seashore. For lava to have flowed that far lava tubes probably formed but did not drain at the end of the eruption so no trace remains.
(see Lava Tubes)

Mt Rouse - page 2

Other lava from Mt Rouse formed the stony rises; these are irregular humps and hollows of broken ground covered with stones. They formed as moving lobes of lava which crusted over then burst as more lava pushed from behind; the burst lava spreading further as new lobes. Lava pressure upwards raised some lobes while lava draining from other parts formed hollows.
Several quarries have extracted scoria from around the base of Mt Rouse. One quarry beside the entrance road is accessible. The walls of this quarry show several metres of mainly black scoria. There is also a thin layer of rock above the main scoria layer where lava flowed over the scoria towards the end of the eruption.

Scoria in a quarry at the base of Mt Rouse.

Scoria from the quarry wall showing the gas bubbles which formed in liquid lava after it was ejected from the vent and before it landed on the crater wall.